Holographic Dark Energy

TL;DR

This paper reviews holographic dark energy (HDE), exploring its theoretical foundations, properties, observational constraints, and extensions within modified gravity theories, aiming to understand dark energy through the holographic principle.

Contribution

It provides a comprehensive review of HDE, including its derivation, properties, observational tests, and its integration with various modified gravity and scalar-field models.

Findings

HDE model based on future event horizon as characteristic length.

Constraints from cosmological observations support HDE viability.

Interactions and modifications in gravity theories are compatible with HDE.

Abstract

We review the paradigm of holographic dark energy (HDE), which arises from a theoretical attempt of applying the holographic principle (HP) to the dark energy (DE) problem. Making use of the HP and the dimensional analysis, we derive the general formula of the energy density of HDE. Then, we describe the properties of HDE model, in which the future event horizon is chosen as the characteristic length scale. We also introduce the theoretical explorations and the observational constraints for this model. Next, in the framework of HDE, we discuss various topics, such as spatial curvature, neutrino, instability of perturbation, time-varying gravitational constant, inflation, black hole and big rip singularity. In addition, from both the theoretical and the observational aspects, we introduce the interacting holographic dark energy scenario, where the interaction between dark matter and HDE is taken into account. Furthermore, we discuss the HDE scenario in various modified gravity (MG) theories, such as Brans-Dicke theory, braneworld theory, scalar-tensor theory, Horava-Lifshitz theory, and so on. Besides, we introduce the attempts of reconstructing various scalar-field DE and MG models from HDE. Moreover, we introduce other DE models inspired by the HP, in which different characteristic length scales are chosen. Finally, we make comparisons among various HP-inspired DE models, by using cosmological observations and diagnostic tools.